Investigation of the photochemistry and quantum yields of triazines using polychromatic irradiation and UV-spectroscopy as analytical tool

Photochemical reactions of atrazine, propazine, simazine, terbuthylazine, ametryn and atraton were investigated in aqueous and buffered (pH = 7-9) solutions (containing a few percent of acetonitrile) using a polychromatic Xe light source at T = 22°C. For terbuthylazine the photochemistry is investigated in detail, including solvent-, temperature-and pH-dependence and products found. The role of polychromatic light sources used in investigations of the photochemistry of triazines is discussed. For the first time, quantum yield measurements were performed in the UV-band between 240-300 nm of the chlorotriazines and ametryn. Isosbestic points were found in the UV-spectra at different irradiation times, and UV-spectroscopy was used to obtain kinetic information. Quantum yields in aqueous solutions at T = 22°C for the chlorotriazines (Φ = 0.048-0.062) and for ametryn (Φ = 0.043) are comparable. The temperature dependence of the photoreaction of terbuthylazine leads to an activation energy of about 13 kJ mol^-1. Quantum yields in acetonitrile and hexane for terbuthylazine are about half of the values found in aqueous solution. Atraton was not degradable under the conditions used, and the quantum yield could only be estimated to be Φ < 0.002.